FORMAL METHODS INTRODUCTION

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1 PROFESSOR (MANY YEARS COLLABORATION IN PARTICULAR WITH JOHN FITZGERALD) UNI VERSITET

2 WHO AM I? Professor Peter Gorm Larsen; MSc, PhD 20+ years of professional experience ½ year with Technical University of Denmark 13 years with IFAD 3,5 years with Systematic 7 years with Aarhus School of Engineering Reviewer for EU on Research projects and applications Consultant for most large defence contractors on large complex projects (e.g. US Joint Strike Fighter) Relations to industry and academia all over the world Has written books and articles about VDM See for details 2

3 Formal Methods Characteristics Formal Methods Europe Tool Support for FM 3

4 WHAT ARE FORMAL METHODS? Formal Methods refers to the use of techniques from logic and discrete mathematics in the specification, design and development of computer systems and software. Mathematics is NOT as difficult as many thinks Mastering of complexity using abstraction. Reduce argumentation to a calculation which can be checked by mechanical means. Replace manual reviews with a repeatable analysis. Formal methods can be used at different levels of rigour. 4

5 VALIDATION TECHNIQUES Inspection: organized process of examining the model alongside domain experts. Static Analysis: automatic checks of syntax & type correctness, detect unusual features. Testing: run the model and check outcomes against expectations. Model Checking: search the state space to find states that violate the properties we are checking. Proof: use a logic to reason symbolically about whole classes of states at once. 5

6 LEVELS OF RIGOUR Level 1: Use of concepts and notation from discrete maths Level 2: Use of formalized abstract specification languages with some mechanized support tools Level 3: Verification of the abstract precise specification Level 4: Fully formal development (refinement from abstract specifications) 6

7 MODELLING COMPUTING SYSTEMS 7

8 MODELLING COMPUTING SYSTEMS In other engineering disciplines (Mechanical, Electrical, Aeronautical etc.) system models are built to help gain confidence in requirements and designs. For example: wind tunnels, stress models Two characteristics of these models are crucial to their successful use: abstraction and rigour. 8

9 ABSTRACTION Engineering models omit details that are not relevant to the purpose of the model. For example: Windtunnel assess aerodynamics Cockpit mockup assess human factors, train pilots The omission of detail not relevant to a model s purpose is called abstraction. The choice of which details to omit is a matter of engineering skill. See for example: Abstraction the key to Computing?, by Jeff Kramer 9

10 ABSTRACTION Compare these extracts from two descriptions of the same system. The FlightFinder System is to be used by travel agents and their customers. Details are entered, including point of departure, destination, preferred dates and times. The system will respond with a range of itineraries and fares, along with the relevant restrictions. What The system records locations as nodes in a connected graph structure. Each node struct contains an array of pointers to reachable destinations plus, for each pointer, a timetable of flights stored as a hash table. Each record in the hash table has a flight number (8 character string), departure and arrival times (standard time formats) and operating dates (standard date format). To obtain the optimal route, the graph must be traversed using a shortest path algorithm on a modified adjacency matrix... How 10

11 RIGOUR The most important property of a model of a computing system is its suitability for analysis: must be objective (not down to the opinion of individual engineers) repeatable susceptible to machine support. The language in which a model is described should be rigorously defined: little room for disagreement about what a model actually says analysis tools reach the same conclusion about model s properties 11

12 MATHEMATICAL REPRESENTATION OF SOFTWARE Formal specifications are expressed in a mathematical notation with precisely defined vocabulary, syntax and semantics. Algebraic approach The system is specified in terms of its operations and their relationships. Model-based approach The system is specified in terms of a state model that is constructed using mathematical constructs such as sets and sequences. 12

13 CLASSES OF FORMAL METHODS Model-based approaches (VDM, Z, B) Algebraic approaches (Act One, Larch, OBJ) Process algebras (CSP, CCS) Logic-based approaches (RTL, TLA) Reactive approaches (Petri-nets, SDL, SAO) Combinations like RAISE (VDM + CSP) and LOTOS (Act One + CCS). ISO standards for VDM, Z, LOTOS and ITU standard for SDL Different strengths Very different kind of tool support 13

14 FORMAL METHODS IN ACADEMIA Tradition with Abstract Models in Europe Focus on Formal Development US focus on Automatic Verification FM taught at many European Universities Spreading from the UK Japan usage and supply gaining strength Different opinions about way ahead (e.g. Parnas, Really rethinking formal methods, IEEE Computer January 2010) 14

15 Formal Methods Characteristics Formal Methods Europe Tool Support for FM 15

16 FORMAL METHODS EUROPE FME = Formal Methods Europe Stimulate the use of formal methods by industry. Promote international co-operation among researchers and users of formal methods. Exchange ideas & identify common interests. Provide links between research and application areas. Conference approximately every 18 months 16

17 FME (VDM) CONFERENCES Brussels, Belgium (1987) LNCS 252 Dublin, Ireland (1988) LNCS 328 Kiel, Germany (1990) LNCS 428 Noordwijkerhout, Netherlands (1991) LNCS 551/2 Odense, Denmark (1993) LNCS 670 Barcelona, Spain (1994) LNCS 873 Oxford, UK (1996) LNCS 1051 Graz, Austria (1997) LNCS 1313 Toulouse, France (1999) LNCS 1708/9 Berlin, Germany (2001) LNCS 2021 Copenhagen, Denmark (2002) LNCS 2391 Pisa, Italy (2003) LNCS 2805 Newcastle, UK (2005) LNCS 3582 Hamilton, Canada (2007) LNCS 4085 Turku, Finland (2008) LNCS 5014 Eindhoven, Netherlands (2009) LNCS 2850 Limerick, Ireland (2011) LNCS 6664 Paris, France (2012) LNCS 7436 Singapore (2014) 17

18 Formal Methods Characteristics Formal Methods Europe Tool Support for FM 18

19 FORMAL METHODS TOOL SUPPORT VDMTools from SCSK Atelier-B from ClearSy FDR from Formal Systems Europe SCADE from Esterel Technologies Lots of prototype/academic tools Overture open-source development for VDM 19

20 FORMAL METHODS TOOL FEATURES Syntax checking Type checking Proof obligation generation Proof support Model checking Pretty printing Animation/Execution Refinement Test automation Code generation Graphical User Interface 20

21 Validation Test Automation Syntax Check Development Interpreter (with debug features) Type Check Available External Executable Code Editor with Syntax Highlighting Prototype available Under development Real-Time Log Viewer Model Checking AST Refactoring Code Generation: C++, Java Not yet started Automatic Proof Reverse Engineering Proof Obligation Generation GUI Generators UML Verification Interactive Proof SysML AADL Translators

22 TAKE AWAY POINTS There is nothing magic about formal methods It is just a sensible engineering approach Strong European FM supplier side USA still strongest on model checking for hardware Japan usage and supply gaining strength Tools are essential for success Consider attending FM 2014 in Singapore

23 THANKS FOR YOUR ATTENTION Any questions? 23